Time delay switching apparatus



Oct. 2, 1956 R. P. GRAEF TIME DELAY swITcHING APPARATUS Filed July 6,1953 /N VE N TOR RP. GRAEF ATTORNEY TIME DELAY SWITCHING APPARATUSRobert P. Graef, Morristown, N. J., assignor to Bell TelephoneLaboratories, Incorporated, New York, N. Y., a corporation of New YorkApplication July 6, 1953, Serial No. 366,177

7 Claims. (Cl. 317-132) This invention relates to a time delay switchingapparatus and particularly to such apparatus for providing a time delayperiod which is variable in response to a change of an operatingcondition.

An object of the invention is to provide an improved time delayswitching apparatus.

In accordance with the invention there is provided a switching apparatushaving an armature adapted to engage a pair of spaced contactssuccessively and a thermal responsive element for varying the spacing ofthe contacts.

In a specific embodiment of the invention herein shown and described forthe purpose of illustration, a time delay switching apparatus isprovided for connecting a load circuit to a current supply line afterthe supply line is initially connected to a current supply source andalso for reconnecting the load circuit to the supply line after afailure and subsequent restoration of the current supply. The switchingof the load circuit to the supply line is delayed for a period thelength of which varies in accordance with the length of the periodduring which the current cupply is interrupted or reduced to anabnormally low voltage. The apparatus comprises a first thermal elementforengaging a irst contact when the element is relatively cool. Cu1rentsupplied from the supply line to a heater for the first thermal elementcauses the thermal element to move out of engagement with the iirstcontact and into engagement with a second contact. The heater, currentis interrupted in response to the energization of an electromagneticrelay by current from the supply line when the thermal element engagesits second contact, thus causing the thermal element to cool and returnto its tirst contact. The electromagnetic relay remains oper-ated bycurrent supplied through a lock-up circuit from the supply line. There-engagement of the first contact by the thermal element completes acircuit through a contact of the electromagnetic relay for operatingacontatcor. The contactor, when operated, connects the load circuit tothe supply line. A second thermal element is provided for moving thefirst Contact toward the second contact in response to a temperatureincrease of the second thermal element and vice versa. A heater for thesecond thermal element is connected to the load circuit so that, whencurrent is being supplied to the load circuit, the heater for the secondthermal element is energized to cause the second thermal element to movein a direction to decrease the spacing of the contacts. When a powersupply interruption of short duration occurs, for example, the spacingof the first and second contacts is relatively small. As a result, thereis a relatively short delay between the time that the current supply isrestored and the time that the load circuit is reconnected to the supplyline.

- Fig. l of the accompanying drawing is a schematic view of a currentsupply circuit embodying the invention; yand Figs. 2, 3, 4 and 5 areschematic views of modifications of a portion of Fig. 1.

United States Patent() ice Referring to the drawing, there is provided aload circuit comprising a rectifier tube 10 having a thermionic cathode11 and an anode 12 for rectifying current Yfrom an alternating-currentsupply source 13 `and for supplying the rectified current to -a load 14across which is connected a filtering condenser 15. There is provided atransformer 16 having a primary winding 17 and secondary windings 18 and19. A switch 20 is provided for connecting the supply source 13 to thetransformer primary 17. When the switch 20 is closed, current issupplied through secondary transformer winding 18 to the cathode 11 forheating the cathode to bring it gradually to its normal operatingtemperature. Closure'of switch 20 also causes an lalternating voltage tobe induced in the secondary transformer winding 19, this voltage beingirnpressed across the supply line 21, 22. One side, 22, of the supplyline is connected directly to a terminal 23 of the load circuitcomprising the rectifier 10 and the load 14. There is provided acontacter 24 having an armature 25 and a fixed contact 26. The armature25 is connected to the other side, 21, of the supply line and thecontact 26 is connected to a terminal 27 of the load circuit. W-hen thecontacter `or relay 24 is de-energized, the armature 25 is spaced fromthe contact`26 and the load circuit is `disconnected from the supplyline. When the relay 24 -operates to cause the armature 25 to engage thecontact 26, the supply line is connected to the load circuit and currentflows from one terminal of secondary transformer winding 19 through thesupply line 21 and through the armature 4and contact of relay 24 to theanode 12 of the rectifier tube 10 and, from the cathode il of the tube,through the load14 to terminal 23 and thence through the supply line 22to the other terminal of secondary winding 19.

There is provided an electromagnetic relay 30 having an armature 3l andcontact 32 and a make-before-break spring combination comprising anarmature 33 and contacts 34 and 35. Two bimetallic thermal elements 38and 39 are provided. An electric heating element 40 is Wound about orotherwise suitably associated with the thermal element 3S. A similarheater 41 is provided for the thermal element 39. The thermal element orarmature 38 engages a contact 42 when no heating current `is beingsupplied to the heater 40. The thermal element 38 is deflected inresponse to heat supplied by the heater 40, when energized, so that thethermal element 38 moves into engagement with the contact 43. Thecontact 42 is secured to the thermal element 39. Heating currentsupplied to the heater 41 cau-ses the thermal element 39 to deiiect soas to move the contact 42 toward the ixed contact 43. The spacingbetween contacts 42 and 43 is thus decreased. One terminal of heater 40is connected to the supply line 22 and its other terminal is connectedthrough contact 35 to the supply line 21. The heater 41 is connectedacross the load circuit, one terminal of the heater being connected toterminal 23 and the other terminal of the heater 41 being connected tothe terminal 27.

When the switch 20 is closed, heating current is supplied from secondarytransformer winding 18 to the cathode 11 of tube 10. At the same timecurrent is supplied from transformer winding 19 to the heater 40 throughacircuit comprising the supply line 21, 22 and contact 35y relay 30 isthus closed through armature 33 land contact i 34 to the supply line 21.When armature 33 engages contact 34, the energizing circuit for theheater 40 is opened at Contact 35. The thermal element 38 thus cools andmoves to re-engage the contact 42. When this occurs, an energizingcircuit for contactor relay 24 is completed from supply line 21, throughthermal element 33, contact 42, thermal element 39, armature 31 andcontact 32 of relay 30 and the winding of contactor 24 to the supplyline 22. Contactor relay 24 thus operates to move its armature 2S intoengagement with its contact 26, thereby connecting line 21 to terminal27 of the load circuit. Current may then ow from line 21 through thespace current path of rectifier tube and through the load 14 to the line22.

When the supply line 21 is connected to the load circuit through thearmature 25 and contact 2d of relay 24, current is supplied. to theheater 41 for the thermal element 39, the heater 41 being connectedacross the load circuit. Asa result, the thermal element 39 is deiiectedto move contact 42 toward the contact 43. The spacing of contact 42 withrespect to contact 43 is thus decreased. If, subsequently,l the supplysource i3 should fail, relays 3d and 24 will release, the heater 41 willbecome de-energized and thermal element 39 will cool to increase thespacing of contacts 42 and 43. When the supply source is restored, thethermal element 38 will move from contact 42 to contact 43 to completean energizing circuit for relay 3? and then the thermal element willreturn to contact 42 to cause the completion of an energizing circuitfor relay 24, as previously described. Thus the time required forconnecting the load circuit to the supply line after restoration ofthecurrent supply is equal to the time required for the thermal element 38to move from contact 42 to contact 43 and back again to contact 42. Thistime interval is dependent upon the spacing of contacts 42 and 43 which,in turn, is dependent upon the temperature of the thermal element 39.

If the interruption of the current supply is very brief, the temperatureof the cathode 1l and the temperature of the thermal element 39 willhave decreased only slightly and the spacing` of contacts 42 and 43 willbe relatively small at the time that the current supply is restored.Therefore, the time required, after restoration ot the current supply,for the thermal element to travel from contact 42 to` contact 43 andback to contact 42 will be relatively short and the load circuit will beconnected to the supply lineV after a brief delay period following therestoration of the current supply. If the interruption of the currentsupply is somewhat longer, the cathode 11 and the thermal'k element 39will have cooled to relatively lower temperatures and the spacing ofcontacts 42 and 43 will be somewhat longer at the time of restoration ofthe current supply. Inthat'case, the delay in connecting the loadcircuit to the supply line after restoration of the current supplywillalso be longer. Thus the flow of space current through the anode-cathodepath of the tube it? is delayed until the cathode has been heated tooperating temperature, this delay period increasing as the period ofinterruption of the current supply is increased. When the period ofinterruption is sufficiently long that the thermal element 39 is cooledto the ambient temperature, the contacts 42 and 43 are spaced a maximumdistance and a maximum delay period is introduced between the time ofrestoration of the current supply and the connection of the load circuitto the supply line. Of course, the time delay switching circuit willfunction not only when a complete interruption of the power supplyoccurs but also whenthe failure is such that the voltage across thesupply line is reduced suiiiciently to cause relays 3u and 24 torelease.

In Fig. 1, when current is supplied to the heater 4l, and, as a result,the thermal element 39 is deflected to move the Contact 42 toward thecontact 43, the thermal element 39 must supply suricient force throughthe contact' 42V tothe thermal element 38 to-deect the thermal element33 toward the contact 43. ln some cases it may be: preferable to providea modified arrangement for conl trolling the spacing of contacts 42 and43 such as is shown in Figs. 2, 3, 4 or 5. In each of thesemodifications there are provided, as in Fig. l, a thermal element 33operating between contacts 42 and 43, a heater 40 for thermal ele` ment38, a thermal element 39 and a heater 41 for thermal element 39. Whenany one of these modifications is substituted for the correspondingportion of Fig. l, one terminal of heater 49 is connected to the supplyline 22 and its other terminal is connected to contact 35, the heater 41is connected across the load circuit, contact 43 is connected to acommon terminal of the winding of relay 30 and armature 33 and thermalelement 38 is connected to the supply line 21. In Figs. 2 and 3 thecontact 42 is directly connected to the armature 31 while in Figs. 4 and5 the contact 42 may be connected through a portion at least of thethermal element 39 to the armature 31. ln Fig. 5 the contact 43 may beconnected to the common terminal of the Winding of relay 39 and armature33 through a portion at least of a thermal element 82.

In Fig. 2 there is provided a member 50 of insulating material to whichthe contact 42 and the thermal element 38 are secured. The member 5t? ismounted on a support 51 by means of a hinge 52 or other suitable deviceso that the member 50 may be displaced about an axis 53. One end ofthermal element 39 is secured to the support 51 and its other end iscoupled through a suitable mechanical linkage 54 to the member 50.Deflection of thermal element 39 in response to current supplied to theheater 41 will thus move the member Sti about the axis 53 in a directionto cause the contact 42 and the thermal element 38 to move togethertoward the fixed contact 43. The contact pressure between thermalelement 33 and contact 42 remains substantially constant when thethermal element 38 is at ambient temperature. The heating of thermalelement 38 by current supplied to the heater 4() will move the element38 out of engagement with the contact 42 and into engagement with thecontact 43.

As shown in Fig. 3, a member 60 of insulating material is secured to theupper end of thermal element 39 and the lower end of thermal element 39is secured to a support 61. The contact 42 and the lower end of thermalelement 38 are each secured to the insulating member 60. Heating of thethermal element 39 due to current supplied to the heater 41 will deilectthe thermal element 39 to move the contact 42 and the thermal element 38together toward the contact 43. Heating of thermal element 38 by currentsupplied to the heater 40 will cause the thermal element 38 to bedeected so as to move it out of engagement with contact 42 and intoengagement with contact 43.

In Fig. 4, the lower ends of thermal elements 38 and 39 are secured to asupport 7l. The heater 41, when energized, supplies heat to both thermalelements 38 and 39 while the heater 4t), when energized, supplies heatonly to the thermal element 38. For example, the heating winding 41 maybe wound about both thremal elements and the heating winding 40 may bewound about thermal element 38 only. Therefore, when the heater 41 isenergized, the contact 42 and the thermal element 38 are moved togethertoward the Contact 43. The energization of heater 40 will cause thermalelement 38 to leave the contact 42 to move into engagement with thecontact 43.

Fig. 5 is a modification of the embodiment shown in Fig. 4. There isprovided a third thermal element 82 to which the contact 43 is secured.The thermal elements 38, 39 and 82 are each secured at one end to asupport 81. The thermal element 82 is provided for compensating forchanges of ambient temperature. Assuming no temperature change of thethermal elements 3S and 39 due to heat supplied by the heaters 40 and4l, if a change of ambient temperature occurs which would cause thethermal elements 38 and 39 to be deiiected toward the right, as viewedin the drawing, for

example, the ambient temperature change will also cause thermal element82 to move toward the right. Therefore a change of ambient temperaturewill not change the spacing of contacts 42 and 43.

What is claimed is:

1. Switching apparatus comprising a pair of spaced contacts, a thermalelement, means for heating said thermal element to cause it to move froma first of said contacts into engagement with a second of said contacts,means responsive to the engagement of said thermal element with saidsecond contact for interrupting said heating and thereby cause saidthermal element to move from said second contact to said first contactand means responsive to the re-engagement of said thermal element withsaid first contact for decreasing the spacing of said contacts.

2. In combination, a first and a second thermal element, a first and asecond contact, a first heating means for heating said first thermalelement to cause it to move from one of said first and second contactsto the other of said contacts and means for moving said first contactand said first thermal element substantially simultaneously with respectto said second contact, said last-mentioned means comprising a secondheating means for simultaneously heating said first and second thermalelements.

3. In combination, an insulating member, a first contact secured to saidinsulating member, a first thermal element secured to said insulatingmember, a second contact, a first electric heater for heating said firstthermal element to cause it to move from said first contact to saidsecond contact, a second thermal element mechanically coupled to saidinsulating member and a second electric heater for heating said secondthermal element to cause the movement of said first contact and saidfirst thermal element toward said second contact.

4. In combination, a first, a second and a third thermal element, afirst contact secured to said first thermal element, a second contactsecured to said second thermal element, a first electric heater forheating simultaneously said first and third thermal elements to causesaid first and third thermal elements to move simultaneously withrespect to said second thermal element, thereby changing the spacing ofsaid contacts, and a second electric heater for heating said thirdthermal element to cause it to move from one of said contacts to theother.

5. The combination with a current supply source and a load of a firstelectromagnetic relay having a first contact which is closed when therelay is de-energized and a second and a third contact each of which isopen when the relay is de-energized, a second electromagnetic relayhaving :a fourth contact which is open when the second relay isde-energized, a first and a second thermal element, a first and a secondelectric heater for said first and second thermal elements,respectively, a fth contact secured to said second thermal element, asixth contact, a first circuit connected across said supply sourcecomprising said first heater and said first contact in series, thecurrent flowing in said first circuit causing said first thermal elementto move away from said fifth contact into engagement with said sixthcontact, said first relay being connected in a second circuit lacrosssaid supply source through said sixth contact and said first thermalelement in series, thereby causing said first relay to operate to opensaid first contact and to close said second and third contacts, theoperation of said first relay opening the energizing circuit for saidfirst heater to cause said first thermal element to return intoengagement with said fifth Contact, a circuit for holding said firstrelay operated cornfpleted through said second contact and said firstrelay, the reengagement of said first thermal element with said fifthcontact completing :a third circuit across said current supply sourcecomprising in series said first thermal element, said fifth contact,said second thermal element, said third contact and said second relay,thereby causing said second relay to operate to close said fourthcontact, the closing of said fourth contact completing a fourth circuitacross said supply source comprising said second heater and said fourthcontact in series, the resulting energization of said second heatercausing said fifth Contact to move towards said sixth contact, and saidload being connected through said fourth contact to said supply source.

6. Switching apparatus comprising a pair of spaced contacts, an armaturein engagement with one of said contacts, a common support of insulatingmaterial, means for securing said `armature and said one contact todifferent portions, respectively, of said common support, a firstcurrent responsive means for actuating said common support to applysubstantially equal forces to said armature and to said one contact,respectively, to move said armature and said one contact simultaneouslytoward the other of said contacts while maintaining the contact pressurebetween said armature and said one contact substantially constant, and asecond current responsive means for causing said armature to move out ofengagement with said one contact and into engagement with said othercontact.

7. In combination a first and a second thermal element, a first and asecond contact, an insulating member, means for securing said firstcontact to one portion of said insulating member, means for securingsaid first thermal element to another portion of said insulating member,means for mechanically coupling said second thermal element to saidinsulating member, a first heating means for heating said first thermalelement to cause it to move out of engagement Wit-h one of said firstand second contacts and into engagement with the other of said contacts,.and means for applying substantially equal forces to said first contactand to said first thermal element, respectively, to move said firstcontact and said first thermal element toward said second contact whilemaintaining the contact pressure between said first contact and saidfirst thermal element substantially constant, said last-mentioned meanscomprising a second heating means for heating said second thermalelement.

References Cited in the file of this patent UNITED STATES PATENTS1,893,223 Burkle Jan. 3, 1933 1,898,174 Dubilier Feb. 21, 1933 2,101,637Davis Dec. 7, 1937 2,196,380 Biebel Apr. 9, 1940 2,302,603 Davis et al.Nov. 7, 1942 2,446,474 Harrold Aug. 3, 1948 2,502,180 Smulski Mar. 28,1950 2,519,368 Hallerberg Aug. 22, 1950 2,539,206 Robinson Ian. 23, 19512,571,360 Hallerberg Oct. 16, 1951 2,596,152 Johnson May 13, 1952

